Photoelectric counter



Sept. 24, 19 46.

L. R- HUNTER ET AL PHOTOELECTRI C COUNTER Filed Sept. 5, 1942 2Sheets-Sheet l 824/5 %IIR ATTO I P 2 1946- 1.. R. HUNTER ET ALPHOTOELECTRIC COUNTER Filed Sept. 5, 1942 2 Sheets-Sheet 2 mkmmwwk MW UM h Patented Sept. 24-, 1946 PHOTOELECTRIC COUNTER Lyle R. Hunter,Clairton, and Oliver C. Levander, McKeesport, Pa.

Application September 5, 1942, Serial No. 457,480

Claims. 1 In the preparation of bundles of metal sheets and the like forshipment, it becomes necessary 4 to know the number of sheets that arein each bundle. As the sheets move along the line of travel from theshears which cut the strip into the desired length of sheets, at a highrate of speed, counting mechanism must be utilized in order to giv anindication of the number of sheets which pass along the line of travel.

In view of the high rate of travel of the sheets, it is found that allof the mechanical counting devices which are available up to this timeare inadequate to install for the desired purpose of this invention,since the speed of actuation of all such devices is not rapid enough tokeep pace with the travel of the sheets, and it has been found inpractice that every type of mechanical counter that is available hasbeen tried but has been found to be a failure for the intended purpose.

In view of the many failures resulting from the installation of themechanical counting devices, it has been necessary to resort to othermeans for counting the rapidly moving sheets. In view of this necessity,there has been evolved an electrical control system for actuating acounting mechanism, the sensitiveness of the electrical control systembeing such that an accurate counting of the sheets is attained, quiteregardless of the speed at which the sheets travel.

In general terms, the present invention provides a photoelectric cell incircuit with two thyratrdn rectifying tubes, current from which tubes isadapted to actuate a counting mechanism, or other electrical devicesoperable from the current output of the thyratron tubes. This current isa continuously flowing pulsating direct current.

The arrangement of the apparatus is such that light from a suitablesource is directed upon a photoelectric cell through the spaces betweensuccessive sheets moving along an operating line which piles the sheetsin suitable stacks or buntiles for shipment to market. It will beunderstood that a flash of light which is produced between the sheetsand falls upon the photoelectric cell must be sufficiently intense toactivate the photoelectric cell, and consequently, the more rapid is thetravel of the sheets, the greater must be the space therebetween.

The invention will be understood more readily from a consideration ofthe accompanying drawings, wherein:

Figure 1 represents a plan view of sheet handling equipment;

Figure 2 represents an elevation thereof; and

Figure 3 represents a wiring diagram showing the circuits for thecontrol of the mechanism.

From the drawings it will be seen that the reference numeral 5 indicatesa cabinet for a photoelectric control, the cabinet being shown asmounted on a table I which comprises conveying instrumentalities forconveying the sheets to a piler 9. The photocell is activated by lightfrom suitable light sources, such as that indicated at l l. A pluralityof motors [3 drive a conveyor for moving the sheets to the piler, andalso for actuating an auxiliary conveyor l5 which receives discardedsorted sheets from the stock which is being handled by the equipment.

The photoelectric counter, designated at IT, is located conveniently atan operators station l9, and it is controlled in the following manner,reference being had to the diagram of Figure 3.

From this view, a photoelectric cell is indicated at 2 I, the cell 2|being in circuit with a rectifying tube 23 which is positioned in thecabinet 5, and which receives current from a transformer 25, as is shownon the drawings.

The tube 23 is a standard radio rectifying tube, known in the trade asType 80, which receives alternating current from the transformer 25,which current results when the transformer is energized from a suitablesource of 110 volt, cycle alternating current.

Each of the thyratron tubes employed in the system is essentially a hotcathode rectifier in which a control grid 4! has been placed between theanode plate 43 and the cathode filament 45. In conventional operation ofthyratron tubes, the cathode is of special construction, being heatinsulated and of large emitting area, so that even when operated at lowpower it is capable of furnishing thermionic current of a predeterminedspecified number of amperes. With the anode at a definite potential withrespect to the oathode, no ciu-rent will pass until the grid potentialis raised above a certain critical value. When the grid potential israised to this value, an are suddenly starts and the full current flows,limited only by the electron emission of the cathode and the resistancein the anode circuit. Once the arc starts, however, the grid losescontrol and no longer has any efiect on the discharge, regardless of itspotential. The are may be stopped only by removing the anode potential.

In a thyratron tube, the grid can be used to start the current whileapplying an alternating voltage to the anode. The are then goes outevery half cycle while the anode is negative. It

3 will start during the next half cycle only if the grid potential isabove its critical value.

The present invention differs importantly from the foregoing, in thatthe discharge in the thyratron tubes is controlled by the grid, thedischarge being stopped when a space between sheets passes a suitablelight source for energizing the photoelectric cell, this latter, uponenergizing, closing a circuit which enables a direct current negativevoltage to be applied to the grid during the instant that the photocell2| is energized, this voltage being greater than the alternating currentpotential between the anode and cathode.

The resulting interruption of the action of the thyr-atron tube causesan actuation of the counter solenoid in a suitable direction to transmitmotion to the counting device.

As soon as each plate obscures the light source, the photocell H isdeenergized and the thyratron circuit reestablished, this circuit beingclosed during the time interval required for the sheet to travelcompletely across the light source. This time is much longer than thetime of flashes between the plates, and gives an opportunity for any lagin the circuit or counting device to have di appeared before the nextoperation.

In order to obtain full wave rectification, and to increase thesensitivity of the circuit, thereby rapidly actuating the countermechanism by applying maximum rectified current to the countermechanism, two of the thyratron tubes are employed, and there issufficient inductance in. the solenoid coil of the counter to maintainthe operation of the tubes continuous during the relatively long timeintervals that the photoelectric cell is masked by passage of a sheet orplate between the light source and photoelectric cell.

As is shown in Figure 3, the secondary of the transformer 25 isconnected in sections to the elements of tube Thus, one section 26 isconnected to the filament Zl through leads 36, 36 and 38, the section 32of the transformer secondary is connected to plates 25 and 30 of thetube 23 through leads Z and 32, respectively, and transformer section 28energizes the source of light ll.

It will be seen from Figure 3 that with the tube 23 being a Type 80radio rectifying tube, the cathode filament 27 receives 5 volts from thetransformer section 2G, and each of the anode plates 29 and 30 receives350 volts from the transformer section 32, this being tapped at itsmidp-ortion, as is indicated at 44. These specified conditions may bevaried, however, depending upon the type of rectifying tube that may beemployed. Also, the position of the tap 44 may be adjusted, as may benecessary to provide requisite current conditions in the remainder ofthe control circuit, as will be pointed out hereinafter. 7

The tap M is shown as being connected by a conductor .5 and resistance3i to the variable resistance ii? of a potentiometer S5. The resistance38 also is connected through conductor 5%? to a suitable resistance 33,which in turn is connected to transformer section 26 through conductor52, which is connected as shown to the lead 36.

The resistances, in the illustrated embodiment of the invention, mayhave a resistance of 7590 ohms in resistance 3!, to a total of 10,000ohms in resistance 48 and 15,000 ohms in resistance 33. Resistances 3iand 33 are fixed resistances and are employed for protective purposes.These values all may be modified to suit any particular installation.

Potentiometer arm 5 is connected through fixed protective resistance 58and conductor 58 to the cathode 60 of the photocell 2!. The anode 62 isconnected through conductor 6 3 to the grids ll and ll of the thyratrontubes 3? and 39, conductor 64- being connected to the grid il throughresistance 55 and conductor 58, and to the grid ti through resistance $5and conductor 68. The resistances 55 and 06 are employed for protectivepurposes and, in the illustrated embodiment of the invention, have avalue of 4 megohms.

The thyratron tubes Bl and 39 are similar,

, and are provided with cathode filaments B5, 45',

respectively, and anode plates 83, 43, respectively.

These elements are energized from sections of a secondary coil of atransformer 25', which is similar to transformer 25, the primary coils20 and Z! of the transformers 25, 25 being energized from a60-cycle,1l0-volt alternating current supply.

Thus the cathode filaments 45 and 35' are energized by section 26, whichgives from about 2 to about 5 volts, as shown in the diagram, andsection energizes the plates t3 and 3 with 350 volts each. Leads 69, it?connect the transformer section 25 with the cathode filament G5, thefilament t5 being connected across through leads l2, while the ends ofthe transformer section 32' are connected to the anode plates 43, t3,respectively, by conductors 1-6, it, in which are interposedrespectively the resistances 89, 82.

The lead '50 of the cathode filament i5 is connected through conductor8% to conductor 50 at the potentiometer resistance 53, this wire servingas the return line for the photocell 2i and also completing theelectronic circuit through the cathode filament of the thyratron tubes.

The transformer section 32' is tapped at the middle third as isindicated at 8%. Conductor 38 connects the tap 86 to a variableresistance 93 which in turn is connected to a solenoid for actuating thecounter ill. Conductor 92 connects the solenoid to conductor 8 2-.

It will be apparent from the drawings (Figure 3) that two thyratrontubes are employed in order to utilize both of the two alternations ofthe current source thereby producing full wave rectification andincreasing the sensitivity of the.system and render the system fullyresponsive to the high-speed installations to which the system isapplied. There is sufiicient inductance in the solenoid coil of thecounter to maintain the operation of the tubes continuous during therelatively long time intervals that the photoelectric cell is masked bypassage of a sheet or plate between the light source and photoelectriccell. The thyratron tubes being in parallel, deliver a total current tothe counter, which current is the sum of the current outputs of thetubes, thereby producing extremely rapid actuation of the counter. InFigure 3 the filaments 5, :35 are rendered incandescent by alternatingcurrent from the transformer coil 26. The two terminals of thetransformer 25 are connected to the two anode plates 3, 33' and thecathodes are connected to each other, as shown, and to wir 84 of theexternal circuit. Therefore it will be seen that the thyratron tubespass unamplified pulsating rectified current to the counter circuit. Therectified current in the counter circuit exhibits variations whichdepend on those of the supply voltage but there is no interruption. Inorder to reduce these variations and obtain a more uniform rectifiedcurrent through the counter solenoid, advantage is taken of theinductance of the solenoid coil whichassists in such action by smoothingout the pulsations of the rectified current, and prevents stopping ofthe tubes as the current never reaches the zero point.

It is thought to be unnecessary in view of the foregoing explanation todiscuss the circuits in detail. One of the characteristics of thethyratron tubes is that they operate on a difference in voltage betweenthe independent cathode and anode circuits of from 3 to 7 volts, whichvoltage may be considered negative since the arc in the tubes passesfrom the plate to the cathode filament. The voltages of the currentsupply and the value of the resistances til, 82, t5, :8, 58 and 86' mustbe adjusted so as to give this voltage difference between theindependent anode and cathode circuits.

Upon the attainment of this condition, the thyratron tubes operate, anda pulsating direct current passes continuously through the countingdevice ll. But it is desired not to have a continuous current flowthrough the counter, as the latter will fail to operate under thiscondition, but it is necessary to interrupt this current periodicallyresponsively to the spaces between the sheets in order for the countingdevice H to reset to count the sheets accurately.

The interruption of the tubes is effected by impressing on the controlgrids ii, :3 i a negative direct current voltage by a value greater thanthe positive 3 to 7 volt difference between the anode plates andfilaments.

This is accomplished in the following manner.

The anode plates 29 and 38 produce a pulsating direct current from thetube 23, some of this current being conducted through the potentiometer35 and conductor 58 to the photocell 2!, the potentiometer arm 54 beingsuitably adjusted tosupply sufficient voltage for the photocell and alsosupply a voltage to the grids ii, ll of at least 3 to '7 negative voltsgreater than whatever voltage is between the plate and filament of eachtube, when the photocell is operating responsively to light hitting thephotocell through the space-s between the traveling sheets. Thus, forexample, if the voltage between the plate and filament of each tube is150 and the voltage drop across the photocell, for example, is 90 volts,the potentiometer must be adjusted to take care of the 90 volts and toimpress at least from, say 153 volts to 157 volts between the grid andcathode filament in each tube. It will be seen, therefore, that underthese conditions, the rectifying circuit would be required to supply atleast 243 volts through the potentiometer 35. This voltage is a positivedirect current voltage and must be sufiicient to, in effect, change thevoltage differential between the plates and cathode filaments 45, G5 tonegative in order to interrupt the action of the thyratron tubes andobtain a resetting of the counter mechanism during the infinitesimallyshort period of interruption of the thyratron tubes, the countermechanism operating to count upon closing th thyratron circuit.

It will be understood, of course, that the potential on the thyratronanodes and cathodes is an alternating current potential, the action ofthe tubes being controlled by a direct current potential of suitablevalue andclirection applied to the grids of the thyratron tubes; andthis direct current potential is applied only when the photoelectriccell is energized by the flash of light passing between the movingplates.

The photoelectric cell therefore acts as a very rapid circuit maker andbreaker, which is required because of the high speed of travel of thesheets; and each time the photocell is energized, that instant ofenergization interrupting the thyratron circuit to make the latteroperative again to actuate the counter the instant that each of thesuccessive moving plates interrupts the light source; so that thethyratron circuit is closed during the length of time that each sheetpasses over the light source, which is relatively long compared to thelength of time that the photocell is active.

Usually the sheets move on the conveyor at a speed of about 800 feet perminute with a space of inch between the sheets. This means, therefore,that each quarter-inch space between the sheets passes over the lightsource in gg ogo of a minute, or second. That means, therefore, that in,640 second the photocell must energize and enable the grids of thethyratron tubes to interrupt the thyratron circuit, due to potentialdrop across resistance 68a. Then at the expiration of second, thethyratron circuit closes and actuates the counter to count one unit, thethyratron circuit remaining closed and the tubes arcing during the timeinterval that it takes the length of the sheet to pass over the lightsource. Then as the plate moves out from the light source, during thenext 6 second that the photocell is energized, the cycle of operation isrepeated.

It will be seen in view of the high speeds involved thatinstrumentalities must be employed which operate instantaneously withoutlag. The photoelectric cell is free from lag, as are also the rectifyingtube 23 and the thyratron tubes 31 and 39, and the time interval duringwhich the sheets pass over the light source and with attendantde-energization of the photocell enables lag in the solenoid coil of thecounter to be taken up and reset ready for the next counting.

It will be seen from the drawings that the conductor a2 is joined to theconductor 8 at the point 94, at which point there is shown connected aconductor 95, which connects with the conductor es at the point 88. Theconductor 53 is shown as being grounded at lfit through condenser Hi2,this condenser being an optional provision, in certain installations itbeing found to be needed to smooth out the operation of the system. Theconductor line 9 $8 with its resistor Hi4 serves to balance thephotocell and thyratron tube circuits. There is also provided acondenser W5, which is connected across the photoelectric cell 2!, thiscondenser rendering smooth the rectified current from tube 23, whichotherwise would be subject to peak variations,

The values of the respective units indicated on the drawings areillustrative only, they being determined for each change of the loadoperated by the circuit, it being understood that the invention is notlimited necessarily to the particular embodiment herein specificallyillustrated and described.

We claim:

1. An electrical control system which comprises, in combination, asource of light, first and second rectifying instrumentalities forrectifying alternating current, a load device operated by unamplifiedrectified current from the second rectifying instrumentalities, andmeans electrically connecting the first and second rectifyinginstrumentilities including light responsive circuit making gnome-1c:

and. breaking means; for:- transmitting at; inter-' vals ofinfinitesimal duration unamplified; recti.-- fled current;- from the.first. rectifying instrumentalities to: the secondrectifying.instrumentalities,. the. said light-responsive circuitmaking, and: breakingmeans' being adaptedfio. be completely masked;from:the source: of light over relatively long. periods of time, but beingexposed to; light from. the light source duringinfi'nitesimally. shorttime intervals between the. relatively. long periods of masking, theresulting transmitted current. being of: a potentialandpolarity'suitable, to pre. determinately'interrupt action. ofathesecondlrecstifying' instrumentalities for actuating the. said. loaddevice.

2. An electricalcontrol system, which comprises the-combination.witha.sourceiof-light, ofa photo 7 electric cell. adapted to; becompletely masked from. the source of; light; over relatively longperiods of, time, but being. exposed to lightiro'm: the-light source:duringinfinitesimally short-time. intervals between. the. long.periodsof. masking, the saidxphotoelectric cellbeingthereby rendered:conductive; by infinitesimally short light flashes: resulting from thelight. passing." tov the; cell be.- tween'the masking periods,firstandsecond rectifying instrumentalities for rectifying. alternating:current,.the first rectifying. instrumentalities producing. a pulsating.unamplified unidirectional. current, a; load. operated. by current fromthe second; rectifying. instrumentalities;. the said second. rectifying.instrumentalities including rectifying tubemeansincluding an: anode; acathode, and a.contr.ol grid, the said anode: and cathode beingconnectedtorsuitablet supplies of alternating current; the: rectifyingitubemeansheing adapted. to; deliver-an unamplified pulsating: direct.current to.the said'load, means connecting the first;rectifying.instrumentalities.in: circuitwith: the control f grid,'.tl1e.connecting means including the: said; photoelectric. cellwhich. isinstantaneously: operable. responsively toxinfinitesimally short;exposure: to light from the; light. source, thephotoelectric: cell beingadaptedxto: clcseithe: circuit: through the grid duringthe,infinitesimally'short exposuresto the; light; and to: open. the:circuit. when; rendered: non-conductive duringzthezrelatively long;periods during, which: the cell is. masked-.froini the light; source,therce'll thereby. transmittingtothe con--- trol; grid during."successive; infinitesimally' short periods :ofconductivity'of thecell a"direct current; of. a. potential and polarity suitable" to: neutralize;alternating current potentials. between the: anode.- and cathode of.therectiiying tube means" toine' terrupt: action of there'ctifyin'g:tube means for actuating the load device incident to: restarting the.rectifying tube means.

An electrical controlsystem whichcomprisesthe combination with a sourceoflight, of 'a photo-- electric cell adapted to be completely maskedfrom the source of. light during relatively long periodsof time whilebeing'exposed to light from thelight source during infinitesimallyshort-time intervals bctweenthe long periods of" masking, the saidphotoelectric-cellbeing thereby rend'ered conductive by infinitesimallyshort light flashes resulting from the light passing to the celliduringinfinitesimally short intervals;betweenithemasking periods, a rectifyingcircuit adaptedrto deliver an unamplified pulsating. unidirectionalcurrent from an alternating current supply; atthyratron type'rectiiyingcircuit comprisinga pair. ofzthyratron-typetubes, the. said: tubes;beingadapted to. utilize both half Waves of: each: alternating: C1113- rentcycle, the: thyratron-type: tubes. including an;

anode,. a. cathode,-.andv a control grid,, the.- anode: and cathodeof;eachtub being. connected to-a. suitable source of alternating current.and the. cathodesbeing, connected together, whereby thetubes are.adaptedto deliver an unamplified. puleating. unidirectional. current, aload deviceadapted to receive the said-.unamplified pulsating;unidirectional current, means includingthesaidv photoelectriccell forconnecting the. grid: of; each of the: said thyratron-type tubes withthe said.

rectifying1circuit,.thephotoelectric cell beingjren--dercdirstantaneously responsive to an infinitesie mally short: flashoflight passing .from the. light. source to the photoelectric cell, thesaid photo:- eleotric cell beingadapted to closeacircuit. from: the.rectifying circuitthrough the, grid of each. thyratronetype. tube duringthe: infinitesimally' shortmoments of conductivity.- of. the.photoelectric; cell and to. open the circuit during relatively longintervals duringwhichthe cell is:completely; masked, the said cellduring successivemoments; of conductivity transmitting. to; the gridsof. the

thyratronetype. tubes a succession. of. momentary:

unamplified: unidirectional; currents. control.

meansior the:said unidirectional current sothat,

current. of. a. potential and. polarity will be impressed on .the gridssuitable 1 to neutralize. alter.- nating; current; potentials between.the: anode. and. cathode. of eachof thethyratron-typa tubes. forinterrupting actioniof the-tubes, thereby momen tarlly actuating theload device toconditionthe; same. for; further actuation through a;succeeding relatively long period of masking. of. the photoelectriccell,the load device being:thus;conditioned.

each time: amomentary flash of light reaches the; photoelectric cellfrom thelightsource;

can. electrical. control; system which comprises-the combination Withiasource-or light,.of a photoelectric cell adapted to be completelymasked. from: the: source. of light. over relatively. long periodsof.time; but being exposed. to. light. from. the lightsource. duringinfinitesimally' short, time intervals between thee long periods. of;mask.- ing, the saidphotoelectric cell being'thereby rem.

dered. conductive by;v infinitesimally short; light:-

flashes: resulting: from: the light. passing, to. the: cell between.the? masking periods. a rectifying: circuit including. a transformer;and a. trioide. rec.- tiiyin'g; tube. having diode; characteristics at:any

. givenrinstantior obtaining full wave rectificationg.

the. said. circuit; being adapted: to deliver an une amplifiedunidirectional current,. second. rectifying instrumentalitiesincludinga' second triode; rectifying circuit. including a second transformer.

1: and. a. pair: of i triodethyratron-type. tubes con.-

nected to sections; of the: said. transformer and. adapted toproducefulllwave. rectification, a load. device operated by'unamplified':rectified current from thextliyratron-type'tubes,.thesaid-rectifyingcircuit being connected. through the photoelectric: cell.to: a control gridof each of: the triode. thyra'e tron-type; tubes. forimpressing: momentary= unidirectionalcurrentto the saidgrid: of each ofthe; triode: thyratron type' tubes for interrupting alternating. currentdischarge. between the re:- maihing? elements. of; the tubes:respon'sively to momentary conductivity of the. photoelectric: cellduring infinitesimally short intervals of'time, the photoelectriccellthereby momentarily closing the rectifying. circuit through.thesaidi control grid in the thyratronetype'tubesi forinfinitesiimall'y. short'iperiodsiof time as.light;flashes toitlie:photoelectric" 0811,; thereby momentarily: rendering. thesaidgcellconductive-rand deenergi'zing. the load device; responsively to: theinfinitesimally' short interruptions to actuation of the thyratron-typetubes, the said tubes supplying unamplified unidirectional current tothe load device during relatively long periods of time during which thephotoelectric cell is completely masked from the light source, thethyratron-type tubes being connected in the circuit to be self-starting,the load device being conditioned for further operation during theinfinitesimally short moments of actuation of the photoelectric cell.

5. Mechanism for counting rapidly moving, closely spaced-apart metalsheet, which comprises the combination with a conveyor having the sheetsto be counted traveling thereon, of a source of light positioned on oneside of the conveyor and adapted to illuminate the sheets and spacestherebetween, a photoelectric cell mounted relative to the conveyor forreceiving infinitesimally short flashes of light from the light source,the said infinitesimally short light flashes being the light passingthrough successive spaces between the rapidly moving sheets, thephotoelectric cell being completely masked from the light source bypassage of the sheets, first and second rectifying instrumentalities forrectifying alternating current, the first and second rectifyinginstrumentalities being free from mechanical and electrical inertiaeffects, the first rectifying instrumentalities being a rectifyingcircuit including a transformer and a triode rectifying tube havingdiode characteristics at any given instant for obtaining full waverectification, the said circuit being adapted to deliver an unamplifiedunidirectional current, the second rectifying instrumentalitiesincluding a second triode rectifying circuit including a secondtransformer and a pair of triode thyratron-type tubes connected tosections of the said transformer and adapted to produce full waverectification, a load adapted to be operated through 10 a predeterminedcycle by unamplified unidirectional current from the thyratron-typetubes, a potentiometer, the said first rectifying circuit beingconnected through the potentiometer and the photoelectric cell to acontrol grid of each of the thyratron-type tubes for impressingmomentary unamplified unidirectional current to the said grid of each ofthe triode thyratron-type tubes for interrupting alternating currentdischarge between the remaining elements of the tubes responsively tomomentary conductivity of the photoelectric cell during infinitesimallyshort intervals of time as light flashes between the sheets beingcounted to render conductive the photoelectric cell, thereby energizingthe load during each flash responsively to the infinitesimally shortinterruptions to actuation of the thyratron-type tubes, the said tubessupplying unamplifled rectified current to the counting means duringrelatively long periods of time during which the photoelectric cell iscompletely masked during passage of the sheets between the light sourceand the photoelectric cell, the said load performing a resettingoperating during the periods of actuation of the thyratron-type tubes,and being actuated to perform the said predetermined cycle during theinfinitesimally short interruptions of the thyratron-type tubes as thephotoelectric cell becomes conductive responsive to light flashesbetween the sheets being counted, the thyratron-type tubes beingconnected in the circuit to be self-starting after each interruptionand, being in parallel, the said thyratron-type tubes deliver a totalcurrent to the load which is the sum of the current outputs of thetubes, thereby producing extremely rapid actuation of the countingmeans.

LYLE R. HUNTER. OLIVER C. LEVANDER.

